Towing a trailer comes with a bit of a learning curve. While safely hauling several tons behind your vehicle might seem like the top priority, proper trailer maintenance is just as critical. After all, staying on top of all those moving and electrical parts is the only way to keep your trailer safe, both for you and everyone else on the road.
Trailer lighting is one of the most important systems to understand, since it’s how you signal your intentions to other drivers and help prevent accidents. But setting it up isn’t a one-and-done deal. Sooner or later, your trailer lights will fail. While that can be a frustrating problem to come up against, diagnosing and fixing the issue is usually easier than you’d think.
The Importance of Pre-Trip Checks & Quality Parts
The first step to fixing faulty trailer lights is spotting them in the first place. Waiting for a disgruntled driver or a police officer to let you know something’s wrong is not the way to go. Instead, make it a habit to inspect all of your trailer lights as soon as you hook up to your vehicle. A pre-trip lighting check isn’t just a box to tick; it’s your first line of defense against avoidable accidents and costly fines. Taking a few extra minutes to walk around your setup, hit the brakes, and test your signals can help you catch issues before they cause trouble on the road.
Another way to cut down on trailer light failure is by using quality parts to begin with. We get it—with prices being what they are, it’s tempting to grab the most affordable option on the shelf. But bargain bin lighting products often use cheap wiring, poor insulation, and flimsy components that fail faster than items from trusted brands. We recommend sticking with industry leaders like Curt, Valterra, Reese, Hopkins, and Grote for your trailer wiring and lighting. Keeping your connections clean, and using dielectric grease to promote good contact, goes a long way, too.
What to Do If Your Trailer Lights Aren’t Working
So, what do you do when—during that pre-trip walkaround—you find that one or more of your trailer lights aren’t working? Before you assume it’s time to rewire the entire setup, take a breath. Chances are, the issue is simpler than you think. Just step back and work through these basic troubleshooting steps:
Check Your Connection - Start by confirming you have a good, solid connection between the trailer wiring harness and your vehicle. If the plug is barely holding together, or there’s debris or corrosion on the contacts, this could explain why there’s a problem. If you find any of these issues, clean the connectors, apply a little dielectric grease, and test the lights again.
Check Your Tow Vehicle’s Lights - Next, make sure the lighting works on the base vehicle itself. Simply put: if there’s an issue with the vehicle’s lights, then the trailer’s lights won’t work either. Do a quick walkaround to confirm everything is working as it should. If not, check the relevant switches, bulbs, and fuses. Once that’s resolved, reconnect the trailer and test again. A trailer lighting circuit tester can make this step much easier.
Check Your Bulbs - If the issue seems to be on the trailer side, inspect the bulb itself. Like the harness, it needs a clean, solid connection to operate. Remove the bulb and check for any signs of damage or corrosion. Additionally, the bulb could simply be burned out. Try swapping it with a known working bulb to confirm whether it needs replacing.
Inspect Your Ground - If the bulb is verified to be in good working order, check that the trailer’s ground wire has a good connection. Its location varies, depending on the type of trailer, but it's usually found near the tongue where the trailer connects to the vehicle. A loose or dirty ground wire can interrupt the entire system. Clean the contact point, reapply dielectric grease, and reattach it before testing again.
Verify With Multimeter - If the lights still aren’t working, the next step is to test the contacts with a multimeter. With the bulb removed and the associated light switch activated, touch the multimeter’s red (positive) probe to the center contact inside the bulb socket—the one that supplies power—and the black (negative) probe to a clean metal ground on the trailer frame. If the multimeter shows no voltage when the light should be on, that means power isn’t reaching the socket. You can also use the multimeter’s continuity setting to check the ground connection. Place one probe on the ground terminal in the socket and the other on a bare metal part of the trailer frame. If there’s no continuity, the ground connection is faulty.
Look For Breaks in the Wires - If everything else checks out, it’s time to start inspecting the wiring for breaks. We saved this step for last simply because many trailers hide their wiring inside the frame, making it harder to access, and most owners will want to check for all easy solutions first before pulling the wiring out. Start by inspecting any visible sections of wiring for damage, pinches, or wear. Flex the wire gently to see if the insulation cracks or splits, which could indicate a hidden break. If you suspect an issue in a concealed section, be prepared to remove access panels or trace the wire back from the plug to the lights.
Making Repairs the Right Way
Once you’ve located the break in your trailer wiring harness, it’s important to make the repair properly. If you’re splicing wires together, the most reliable method is a solid solder joint sealed with high-quality heat-shrink tubing. This creates a durable, weather-resistant connection that won’t wiggle loose or corrode over time.
If soldering feels like overkill for a roadside fix or you’re looking for something quicker, then crimp-style connectors with built-in solder are a solid alternative. These work like traditional crimp connectors but include a ring of solder inside the tubing. When heated with a heat gun, the solder melts to bond the wires, and the outer sleeve shrinks down to seal the joint—giving you the strength of solder with the convenience of a crimp.
That said, not every wire is worth saving, so you should know when to repair and when to replace.
A clean, isolated break in an otherwise intact wire? Go ahead and fix it. But if the damage is due to rotting insulation, mouse-chewed sections, or signs of widespread wear, it’s smarter (and safer) to replace the entire harness. Small problems can hide bigger ones, and patching up a bad system often just sets you up for more failures down the road.
Upgrades That Make a Difference
Once you’ve dealt with faulty wiring, it’s worth considering a few smart upgrades that can prevent future headaches and even help improve overall lighting performance.
One of the most effective is a sealed wiring harness. These harnesses protect the wires from moisture, road salt, and general wear, cutting way down on corrosion-related issues. If you’re installing a new setup or replacing an old one, sealed options are well worth the investment.
Plug-and-play harnesses are another great choice, especially if you’re not looking to spend all day under the trailer. These pre-terminated kits make installation fast and foolproof. You just match the connectors, snap them into place, and you’re good to go. They pair especially well with towing systems from brands like Blue Ox and Husky Towing, which offer wiring kits designed to complement their hitches and brake controllers.
And of course, there’s LED lighting. LED kits are not only brighter and more energy efficient, but also more durable and longer-lasting than old-school incandescent bulbs. Many LED systems also feature built-in waterproof housings for extra peace of mind. For quality lighting and wiring solutions, Grote offers a solid lineup that’s engineered with towing reliability in mind.
A little extra effort up front can make your whole setup safer, brighter, and a lot more hassle-free.
Parts Via Is Your Trailer Wiring Headquarters
No matter what kind of trailer wiring fix or upgrade you’re after, Parts Via has you covered. While we offer parts for just about every corner of your vehicle, towing gear is one of our specialties. Our inventory is stocked with the biggest names in the industry—so whether you’re chasing down a single connector or replacing your entire lighting system, you’ll find what you need here.
Even better, our fast, FREE ship-to-store option helps you save on delivery and connects you with trusted local shops that can handle the install for you.
Ready to stop troubleshooting and start towing? Get your parts from Parts Via and hit the road with confidence.